Even then, they were thought to represent variations in solar activity. Paul Mayewski, one of George Denton’s students, was the scientist in charge of coordinating the effort of over 200 scientists in the American Ice Core Program that in 1993 completed the Greenland Ice Sheet Project II (GISP2). A NAO negative phase is produced when the weakening of the Iceland low and the Azores high reduces the pressure gradient resulting in weaker more southern westerlies producing colder conditions over much of North America and Northern Europe while moving the storm tracks southward towards the Mediterranean. They propose solar variability as the forcing behind these oscillations. Under humid conditions trees were unable to grow on wetter bogs. Although Ireland hydrology shows a complex pattern over the increasingly wet Neoglacial trend, lows in the Bray cycle are associated with periods of increased precipitation (figure 54 d). Superimposed on this trend are millennial-scale SST variations coherent with some of the North Atlantic ice-rafting events defined by Bond et al. (2013), and shows that every Bray cycle low coincides with a significant downward departure from the general temperature trend (figure 55 c).